Geodesy (InSAR, GPS, Gravity) and Big Earthquakescais.gsi.go.jp/UJNR/UJNR4P/Simons-Caltech.pdf ·...
Transcript of Geodesy (InSAR, GPS, Gravity) and Big Earthquakescais.gsi.go.jp/UJNR/UJNR4P/Simons-Caltech.pdf ·...
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Mathew PritchardTeh-Ru A. SongYuri Fialko Luis Rivera Mark Simons
Geodesy (InSAR, GPS, Gravity) and Big Earthquakes
UJNR Earthquake Research Panel, Morioka, Japan - Nov 6, 2002
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Goals• Accurate and high resolution fault slip models for big EQs
• Why?– Moment release budget as a function of position– Co-seismic rheology– Earthquake interaction– Input into post-seismic models– Relationship to tectonic geomorphology
• Issues/difficulties– Observational: dataset limitations– Mathematical: Choice of inversion technique– Earth Structure: Spatial variations of rheology
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DecorrelationPhase (multiple LOS)SeismicityAzimuth Offsets
1999 Mw 7.1 Hector Mine EQ
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Implications for post-seismic and interseismicmodels:
ØSignificant vertical fault slip
ØFault slip concentrated at shallow depth
ØMost slip in the northern half
ØApparent slip deficit…
A coseismic distributed slip model
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Integrate slip along strike:ØHalf-space vs. layered elastic structureØShallow moment deficit required by inversion (Mw 6.1)
Cartoon models:ØDifference in models controlled by near field inflection of displacement profile
Conjecture:ØInelastic process causes inflectionØNeeds improved modeling
The apparent slip deficit
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Practical/geophysical lessons:
ØRapid response possibleØ3 components (phase/offsets)ØDecorrelation
-> reveals complex faultingØPermit high spatial resolution modelsØShallow slip deficit
-> inelastic processes?
Horizontal Displacements Field
Still to be done…
ØUse refined coseismic model for postseismic studies (important for periods immediately following EQ).ØData/model comparison tricky
log ||V||
1999 Mw 7.1 Hector Mine EQ
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The deforming continent1992-2000:
Subduction earthquakes•1995 Mw 8.1 Antofagasta•1996 Mw 7.7 Peru•1998 Mw 7.0 Antofagasta•2001 Mw 8.4 Peru ????
Survey of > 900 volcanoes•4 undocumented sources•1 incipient caldera?
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South America: A Land of Big Earthquakes
The Mejillones Peninsula and Atacama viewed from Apollo
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The temporal and spatial pattern of big earthquakes
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The available data: Mw 8.1 1995 and Mw 7.1 1998
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Compare previous models to InSAR
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1995 Mw 8.1: Phase unwrapped
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1995 Mw 8.1: The model
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Methods
• Seismic data:– Teleseismic displacement data (30o<∆<90o)
• 1995 Mw 8.1: 125 seconds, 19 P; 16 SH records• 1998 Mw 7.1: 60 seconds, 18 P; 15 SH records
– Station response, attenuation– Wavelet transform records to optimize spatial and temporal
resolution (Ji et al., 2002)
• InSAR data:– 1995: 5 orbital tracks of data, 12 interferograms (ASC/DSC)– 1998: 2 orbital tracks of data, 5 interferograms (DSC)
• Inversion – 1D layered space model at source (Husen et al., 1999) – Minimize misfit, moment, roughness– Solve for slip amplitude and direction, rise time, and rupture velocity– Simulated annealing algorithm (Rothman, 1986)
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Compare slip inferred from different datasets
⇒For 1998 Mw 7.1 earthquake: seismic and geodeticresults similar (CMT epicenter off by 40 km)
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Compare slip inferred from different datasets
⇒For 1995 Mw 8.1 earthquake: seismic and geodeticresults differ
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•Little seen with InSAR
•Signal mostly due totroposphericcontamination
•InSAR constrains where slip did not happen
Post Seismic?
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Post-seismic deformation visible in GPS data
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Co-seismic andPost-seismic slip
Max slip:1995 Mw 8.1: 5m1998 Mw 7.1: 1 m1 yr Post: 20 cm
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Chile ConclusionsØ Seismic and geodetic slip inversions:
– CMT discrepancy for small, simple event (Mw 7.1, 1998)
Ø Earthquakes appear to mosaic fault plane
Ø Little post-seismic deformation from Mw 8.1 compared to earthquakes of similar size
Ø Future work:– 3 Mw 7’s from the 1980’s– Can tsunami waveforms help constrain shallow slip?– Are there only smaller earthquakes at the bottom of the
seismogenic zone?– Why so little post-seismic slip? – Role of peninsulas?
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Use precise slip models and earthquake catalogs
Use sea surface altimetry (Sandwell & Smith)___________
Averaged subduction zone gravity profilesØVariations
•Age•Convergence rate
ØNo strong correlation with seismogenic behavior
Concentrate on trench parallel gravity anomaly (TPGA)
Earthquakes, gravity, and theseismogenic behavior of subduction zones
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Post 1964 Interseismic Zweck et al
Alaska
Trench Parallel Gravity Anomaly (TPGA)
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Known seismic gap
TPGA forKamchatka/Kurile
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Seismic moment release in equal area TPGA bins
Histograms
Consider EQ catalogs
Caveats: ØLocationØLocationØLocation
Implications:ØSpatial fixityØPredictiveØTsunami potential
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Joint TPGA and TPTA Histograms
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1. Mean level controlled by age, velocity, T…2. Coupling of long term tectonics and seismogenic behavior3. Spatial predictivity4. Tsunamogenic predictivity5. Eventually model-derived bounds on stress variations6. Need better source models for historic EQs
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Ø Wide swath Ø L Band (25cm wavelength)Ø Short revisit times Tight orbital controlØ Small pixels for high strain zones and decorrelation Ø Reduce troposphere/ionosphere artifactsØ Frequent multiple components (asc/dsc/left/right)Ø Global accessØ Constellation -> science and robustnessØ Rapid deliveryØ Free/Cheap data
Ø ALOS• L Band, 45 day repeat, asc only, no US data agreement
Ø ENVISAT• C Band, 35 day repeat, no US data agreement (not free)
The future of InSAR?
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END
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